The field of the invention is electrolytic hydrogen production.
Hydrogen exhibits many advantages as an alternative energy source, including high energy density, and environmentally neutral combustion or recombination with oxygen. Furthermore, hydrogen can be generated from water in a relatively simple process (e g., water electrolysis), with almost no undesirable byproducts. However, despite the conceptually simple generation of hydrogen by water electrolysis, the energy efficiency of water electrolysis remains often problematic, and many approaches have been developed to improve the electrolytic generation of hydrogen.
In one approach, water electrolysis is powered or assisted by electricity generated in photovoltaic cells. The use of photovoltaic cells is particularly attractive, because photovoltaic cells produce voltages and currents suitable for electro-dissociation of water in an environmentally neutral manner. However, industrial scale production of hydrogen supported by photovoltaic cells with current technology would require vast arrays of photovoltaic cells. Moreover, besides a significant space requirement, large arrays of photovoltaic cells would incur a considerable cost.
In another approach, the electrolyte in a water electrolysis cell is heated to achieve improved conductivity. Improved conductivity of the electrolyte generally allows passing higher currents through the electrodes, and thereby increases hydrogen production per electrolysis cell. However, the energy cost to heat the electrolyte often reduces the overall efficiency of the electrolytic process. Furthermore, the use of a heated electrolyte frequently poses various problems due to the chemically aggressive character of some heated electrolytes. Still further, both photovoltaic and thermally assisted electrolysis typically produce hydrogen gas at or near atmospheric pressure. Consequently, when hydrogen needs to be stored or transported, additional energy must be spent to compress or liquefy the produced hydrogen gas.
To circumvent at least some of the problems associated with compression or liquefaction of the hydrogen gas, Smith discloses in U.S. Pat. No. 4,530,744 hydrogen electrolysis under pressure, in which water is pumped into an electrolyzer at an elevated pressure (typically 45 bar), resulting in a compressed hydrogen stream and a compressed oxygen stream. Smith""s hydrogen stream is subsequently liquefied by cooling the hydrogen stream via expansion of the compressed oxygen stream. However. Smith""s process requires a considerable amount of energy to compress the water, which is only partially recovered by expanding the oxygen stream for the cooling process. Moreover. Smith""s electrolyzer requires a pressure resistant configuration, demanding especially thick walls and gas tight joints due to the considerable pressure differences between the inside and the outside of the pressure electrolysis unit.
In order to reduce problems with the pressure differences between the inside and outside of a pressure electrolysis unit. Reynolds describes in U.S. Pat. No. 3,652,431 a submerged electrolyzer in which a submerged hydrogen and a submersed oxygen storage tank with open bottom portions are in fluid communication with an electrolyzer. The water pressure acting on the gases in the storage tanks in Reynold""s configuration is balanced by the line pressure from a non-submerged pump that delivers the electrolyte to the submerged electrolyzer. Although Reynold""s submerged electrolyzer solves various problems with pressure differences between the inside and outside of the pressure electrolyzer, various difficulties still remain. Most notably, considerable energy is required to counter balance the hydrostatic pressure on the submerged electroivzer by pumping the electrolyte into the electrolyzer. This will become especially problematic, when the pressure electrolyzer is submerged at a relatively great depth.
Various technologies are known in the art to improve energy efficiency of water electrolysis, however, all or almost all of them have several drawbacks. Therefore, there is still a need to provide methods and apparatus for improved hydrogen production.
The present invention is directed to an apparatus with a housing at least partially filled with an electrolyte, and a pair of electrodes (i.e., an anode and a cathode) disposed within the electrolyte to split the electrolyte into a first and a second product gas when a voltage is applied.
Both electrodes are disposed in the electrolyte at a depth sufficient for a reduction in electrolyzing energy of greater or equal than 10%. It is generally preferred that the housing is disposed in, or part of, a deep well, or below the surface of a body of water.
In one aspect of the inventive subject matter, the electrolyte comprises water, preferably purified water, and even more preferably deionized water from a reverse osmosis unit. Consequently, a preferred first product gas is hydrogen and a preferred second product gas is oxygen.
In another aspect of the inventive subject matter, the depth at which the electrodes are disposed at is between 300 and 500 meters, and preferably between 500 and 1,000 meters, however depths greater than 1,000 meters are also contemplated.